Exposure control device

ABSTRACT

In addition to a diaphragm, a filter turret is used to control the amount of light passing through a taking lens of a television camera or the like, whereby the range of exposure control is enlarged. When the diaphragm which is automatically controlled comes to its limit, a filter is changed to another filter having different transmittivity.

United States Patent 1 Numata [451 Apr.2, 1974 EXPOSURE CONTROL DEVICE[75] Inventor: SalJuro Numata, Urawa, Japan [73] Assignee: Fuji ShashinKoki Kabushiki Kaisha, Saitama-ken, Japan 221 Filed: Sept. 13,1972

211 App]. No.: 288,884

[30] Foreign Application Priority Data Sept. 14, 1971 Japan 46-7l510[52] U.S. Cl. 250/214 P, 95/10 CD [51] Int. Cl. H0lj 39/12 [58] Field ofSearch 250/214 R, 214 P, 229;

95/10 R, 10 A, 10 B, 10 CE, 10 D, 64 C, 64 D; 178/5.4 E, 17 D, DIG. 29

[56] References Cited UNITED STATES PATENTS 5/1970 Ort 95/10 CD3,651,749 3/1972 De Groot 95/10 CD Primary Examiner-Archie R. BorcheltAssistant Examiner-D. C. Nelms Attorney, Agent, or FirmFleit, Gipple &Jacobson [57] ABSTRACT In addition to a diaphragm, a filter turret isused to control the amount of light passing through a taking lens of atelevision camera or the like, whereby the range of exposure control isenlarged. When the diaphragm which is automatically controlled comes toits limit, a filter is changed to another filter having differenttransmittivity.

7 Claims, 4 Drawing Figures PATENTED APR 2 I974 SHEU 1 0F 2 FIG.|

FIG.2

1 EXPOSURE CONTROL DEVICE BACKGROUND OF THEINVENTION 1. Field of theInvention This invention relates to an automatic exposure controldevice, and more particularly to a device for controlling exposure orlight value over a wide range in a camera.

2. Description of the Prior Art In the field of television andcinematograph, the brightness of an object varies over a great rangeduring its operation. It is strongly desired in the camera used in thesefields to control the exposure or light-value over the wide range of thebrightness variation. It has been very difficult or impossible, however,to control the exposure over such a wide range due to the mechanicalrestriction in designing the television camera, especially in designingthe diaphragm for the taking lens.

SUMMARY OF THE INVENTION The primary object of the present invention isto provide a device for automatically controlling the exposure over awide range in a camera such as a, cinematographic camera, a televisioncamera or the like.

In order to accomplish the above object, the device in accordance withthe present invention utilizes several interchangeable neutral filtersof different density which are automatically put into the optical axisof the taking lens by means of an electric circuit detecting thebrightness of the object so that the light value of the light passingthrough the taking lens can be varied over a wide range.

In this invention, for instance, a filter is changed to a denser filterwhich allows less amount of light pass therethrough when the diaphragmautomatically con trolled by means of a known exposure control meansreaches the minimum limit thereof. Then, at the time when the filter ischanged to a denser one, the size of the diaphragm becomes larger againand starts to be made smaller as the brightness or exposure valueincreases.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF PREFERRED EMBODIMENTReferring to FIGS. 1 to 3 showing the basic principle of the presentinvention, an automatic control diaphragm 1 which is automaticallycontrolled in association with any type of known exposure controllingmeans operated in accordance with the brightness of the object isprovided with two projections 2 and 3 on the periphery thereof. Theprojections 2 and 3 are fixed to a diaphragm control ring and indicatedthe size of the diaphragm by the position thereof. The automatic controldiaphragm 1 is used as a first exposure control means, and is used incooperation with a second exposure control means. The second exposurecontrol means is a filter turret 11 shown in FIG. 2 which has severalneutral density filters l2, l3 and 14 of different density and iscontrolled by a switching means operated by said first exposure controlmeans. The switch means comprises said projections 2 and 3 indicatingthe size of the diaphragm and electrical switching means provided undereffect of said projections.

As shown in FIG. 1, two photocouplers 26 and 36 are provided at thelimit positions of the projections 2 and 3, respectively, so that thelimit of the diaphragm size may be electrically detected. Thephotocouplers 26 and 36 include luminous (light emitting) diodes 25, 35and phototransistors 24, 34 to receive the light from the luminousdiodes 25, 35, respectively. The projections 2 and 3 have an effect ofintercepting the light from the luminous diodes 25, 35 and prevent thelight from reaching the phototransistors 24, 34. Thus, the limits of thediaphragm size is detected electrically by the photocouplers 26, 36.

The first exposure control means is operated in a known manner by animage signal of the television, and the limit positions thereof aredetected and the signal thereof is transmitted to said second exposurecontrol means by means of a switching means comprising saidphotocouplers 26, 36 and Schmit circuits. In more detail, the switchingmeans provides an output to a driving motor control circuit of thesecond exposure control means. I

When the diaphragm 1 comes to its limit, for instance its smaller limit,one of the projections 2 comes to the photocoupler 26 and operates theswitching means to rotate the filter turret l1 and change an N.D. filter12 to a denser N.D. filter 13. When the diaphragm 1 comes to its smallerlimit with the denser filter 13, the switching means again operates torotate the filter turret 11 to further change the filter 13 to a stilldenser filter 14.

The relation between the diaphragm 1 rotation and the exposure or lightvalue is shown in FIG. 3. The diaphragm is made smaller along the lineA-a, first, and when the diaphragm comes to its smaller limit the denserfilter 13 is put into the optical path instead of the filter 12. Thus,the incident light value is abruptly lowered. In response to thisdecrease in the light value, the diaphragm 1 is abruptly opened alongthe line a, 0 Then, the diaphragm l is gradually closed again along theline a b, in the similar manner to the first operation mentioned above.

When the value of light decreases, the operation of the device is justreverse of the above described operation. That is to say, the projection3 makes the photocoupler 36 operate to switch the filter turret drivingmeans in the reverse manner of the above described manner. When thediaphragm 1 comes to its larger limit, the projection 3 intercepts thelight from the luminous diode 35 and operates the switching means torotate the filter turret 11 in the counterclockwise direction andchanges the denser filter 13 to a filter 12 having lower density.

Referring to FIG. 4, the electric circuit serving as said switchingmeans comprises a Schmit circuit including a first control circuit 20having transistors 21, 22 and a set of diodes 23. When the firstexposure control means or said diaphragm comes to its smaller limit,said projection 2 intercepts the light from the luminous diode and thetransistor 24 and accordingly the transistor 22 are cut off from thenormal condition. Then, the transistor 21 is turned on and an output ofa definite level is obtained from a terminal A. The output from theterminal A serves as an input sent into a control circuit for operatingsaid second exposure control means. Thus, the filter turret 11 isrotated clockwise and the denser filter 13 is brought into the opticalaxis of the camera.

The filter turret 11 is provided with projections 12a, 13a and 14a onthe periphery thereof at positions corresponding to said filters 12, 13and 14 to intercept light emitted by a luminous diode 28 in aphotocoupler 29 and cut off the phototransistor 27 therein. Therefore,when the denser filter 13 is brought into the optical axis of thecamera, the projection 13a effects to cut off the photocoupler 29 andaccordingly the Schmit circuit is reversed and the output from saidcontrol circuit 20 is cut off. Accordingly, the operation of said secondexposure control means or said filter turret 11 is stopped and the firstexposure control means or said diaphragm is operated according to theimage signal through the denser filter 13.

To the contrary, when the amount of light is decreased and the diaphragm1 comes to its larger limit, the projection 3 cuts off the light in thephotocoupler 36 and an output of a definite level is obtained from aterminal B. By this output B, the second exposure control means 11 isrotated counterclockwise until the filter 12 of lower density is broughtinto the optical path. When the filter 12 is put into the optical path,the projection 12a corresponding to the filter 12 comes to cut off thephotocoupler 29, which results in reverse of a second control circuit 30similar to the first control circuit 20.

As shown in and apparent from FIG. 4, phototransistors (or transistors)24 and 34 are inserted in series between collectors (a) of thetransistors 21 and 31 and bases (b) of the transistors 22 and 32 in apair of Schmit circuits in said first and second control circuits 20 and30. Accordingly, the Schmit circuit is not reversed even if thephototransistor 34 is turned on im-' mediately after the photocouplers26 or 36 is once cut off by operation of the transistor 24 or 34, butcan be reversed only providing a negative input to the base circuit (c)of the transistor 21 or 31. Further, since condensers 40 and 50 areinserted into base circuits of one of the transistors 21 and 31 of theSchmit circuits, the transistor 22 or 32 is always turned on and theSchmit circuits constitute a stable multicircuit always turned on in thepredetermined direction when a power source is put in. Thus, the firstand second exposure control means are controlled in a stable conditionto effect said operations.

What is claimed is:

1. An automatic exposure control device adapted to be used in a cameracomprising a first exposure control means for controlling the quantityof light passing through the exposure lens of the camera to give acorrect exposure according to the brightness of an object to bephotographed or televised, a second exposure control means including aplurality of filters of different transmitivity and means forselectively bringing one of said filters into the optical path of theexposure lens, and a filter selecting means for selecting one of saidfilters to bring the same into said optical path according to the levelof brightness of the object.

2. An automatic exposure control device as defined in claim 1 whereinsaid filter selecting means comprises means for detecting the upper andlower limits of the control range of said first exposure control means,and

means for changing said filters when said limit detect-- ing meansdetects the limit of the first exposure control means, whereby the rangeof exposure control is substantially increased.

3. An automatic exposure control device as defined in claim 2 whereinsaid first exposure control means is a diaphragm the size of which iscontrolled by rotation of a diaphragm operating ring, said limitdetecting means comprises a light source provided in the vicinity ofsaid ring, a photoresponsive element provided to receive light emittedfrom said light source, and a light intercepting member provided on theperiphery of the diaphragm operating ring to indicate the size of thediaphragm by the position thereof and intercept the light from the lightsource to prevent the photoresponsive element from receiving the lightby coming into the position between the light source and the element,and said filter changing means comprises an electric circuit forenergizing a driving motor to operate said second exposure control meansto select one of said filters according to the output of saidphotoresponsive element.

4. An automatic exposure control means as defined in claim 3, wherein aphotocoupler is used as said light source and said photoreceptor.

5. An automatic exposure control means as defined in claim 4, whereinsaid position regulating means comprises a light source disposed in thevicinity of the periphery of said filter turret, a photoreceptor forreceiving the light from said light source, a light intercepting memberprovided on the periphery of the turret for intercepting the light fromthe light source to prevent the photoreceptor from receiving the lightby coming into such a position to intercept the light as the turretrotates, and means for stopping the rotation of the turret uponinterception of the light by detecting the output of said photoreceptor.

6. An automatic exposure control means as defined in claim 1 whereinsaid second exposure control means is a filter turret having a pluralityof filters of different density arranged around the center of rotationof the turret.

7. An automatic exposure control means as defined in claim 6, whereinsaid filter turret is provided with a position regulating means forselectively stopping the turret at one of predetermined positions tobring one of said filters in alignment with the optical path of theexposure lens of the camera.

1. An automatic exposure control device adapted to be used in a cameracomprising a first exposure control means for controlling the quantityof light passing through the exposure lens of the camera to give acorrect exposure according to the brightness of an object to bephotographed or televised, a second exposure control means including aplurality of filters of different transmitivity and means forselectively bringing one of said filters into the optical path of theexposure lens, and a filter selecting means for selecting one of saidfilters to bring the same into said optical path according to the levelof brightness of the object.
 2. An automatic exposure control device asdefined in claim 1 wherein said filter selecting means comprises meansfor detecting the upper and lower limits of the control range of saidfirst exposure control means, and means for changing said filters whensaid limit detecting means detects the limit of the first exposurecontrol means, whereby the range of exposure control is substantiallyincreased.
 3. An automatic exposure control device as defined in claim 2wherein said first exposure control means is a diaphragm the size ofwhich is controlled by rotation of a diaphragm operating ring, saidlimit detecting means comprises a light source provided in the vicinityof said ring, a photoresponsive element provided to receive lightemitted from said light source, and a light intercepting member providedon the periphery of the diaphragm operating ring to indicate the size ofthe diaphragm by the position thereof and intercept the light from thelight source to prevent the photoresponsive element from receIving thelight by coming into the position between the light source and theelement, and said filter changing means comprises an electric circuitfor energizing a driving motor to operate said second exposure controlmeans to select one of said filters according to the output of saidphotoresponsive element.
 4. An automatic exposure control means asdefined in claim 3, wherein a photocoupler is used as said light sourceand said photoreceptor.
 5. An automatic exposure control means asdefined in claim 4, wherein said position regulating means comprises alight source disposed in the vicinity of the periphery of said filterturret, a photoreceptor for receiving the light from said light source,a light intercepting member provided on the periphery of the turret forintercepting the light from the light source to prevent thephotoreceptor from receiving the light by coming into such a position tointercept the light as the turret rotates, and means for stopping therotation of the turret upon interception of the light by detecting theoutput of said photoreceptor.
 6. An automatic exposure control means asdefined in claim 1 wherein said second exposure control means is afilter turret having a plurality of filters of different densityarranged around the center of rotation of the turret.
 7. An automaticexposure control means as defined in claim 6, wherein said filter turretis provided with a position regulating means for selectively stoppingthe turret at one of predetermined positions to bring one of saidfilters in alignment with the optical path of the exposure lens of thecamera.